The invention relates to articulated booms, and more particularly to articulated booms including an arrangement for leveling the workman support bucket.
A conventional articulated boom comprises a pair of elongated boom portions that are pivotally joined together. The lower end of one of the portions is pivotally mounted on a frame, and the upper end of the other portion supports a pivotally mounted bucket in which a workman rides. The boom also comprises means for leveling the bucket throughout the range of movement of the boom portions. This means typically includes a closed loop of flexible, elongate material, such as a cable or chain, which extends through the boom from the frame to the bucket and which is supported by pulleys or sprockets. A portion of this loop, referred to as the tension portion, resists downward tilting movement of the bucket and thus is maintained under tension by the force of gravity acting on the bucket. The remainder of the loop, called the holdback portion, is not maintained under tension by the bucket.
Articulated booms are commonly mounted on trucks, and it is desirable to maintain tension in the loop so that the bouncing which inevitably occurs when the boom is being transported does not cause the loop to come off its pulleys or sprockets and does not cause damage to the loop itself or to other components within the boom. Maintaining the loop under constant tension also reduces elongation of the loop when it is loaded, such as when a workman enters the bucket.
Houck U.S. Pat. No. 4,429,763 discloses an arrangement in which turnbuckles are provided for adjusting the tension in the loop. A disadvantage of using turnbuckles is that it is necessary to frequently tighten the turnbuckles in order to maintain tension. Another disadvantage of using turnbuckles is that the closed loop is typically enclosed within the boom portions and it is necessary to provide access to the interior of the boom portions in order to afford access to the turnbuckles. For example, in the Houck patent, access plates 13' and 14' are provided to afford access to the turnbuckles. Thus, it is necessary to remove the access plates each time the turnbuckles are tightened.
Attention is directed to the following U.S. Pat. Nos.
______________________________________ Johnson 4,081,055 Mar. 28, 1978 Freudenthal, et al. 4,512,436 Apr. 23, 1985 Houck 4,429,763 Feb. 7, 1984 Brendel 3,049,194 Aug. 14, 1962 Geary 2,063,802 Dec. 8, 1936 Gould 4,484,732 Nov. 27, 1984 Pitts 2,323,352 Jul. 6, 1943 Puryear, et al. 3,302,480 Feb. 7, 1967 ______________________________________